Warning: `auto` in formal parameter

Question

I executed the following program -

#include <iostream>
#include <vector>
using namespace std;

void display(const vector<auto> &arr) {
    for (auto const &val: arr) 
        cout<<val<<" ";
    cout<<endl;
}

int main() {
    vector<int> a (6);
    display(a);

    vector<double> b (3);
    display(b);
    return 0;
}

And it gives the following warning (without any error) -

warning: use of ‘auto’ in parameter declaration only available with ‘-fconcepts’
5 | void display(const vector<auto> &arr) {                                                                                                                          
  |                           ^~~~          

Why am I getting this warning & what is this warning about ?

Should I be using auto in as formal parameter here ??

What can be the alternative way if it's the wrong approach ??

Answer 1

You really want a template:

template<typename T>
void display(const vector<T>& arr)
{
    for (auto const &val: arr) 
        cout<<val<<" ";
    cout<<endl;
}